velocity101

This is a personal hobby project of mine that I haven't been able to make work myself but you electronics guru's should be able to do in your sleep.

I am trying to create an IR sensor array which detects a high-velocity bullet passing through a square frame which is set several yards away. Upon detection, it instantly triggers an Arduino pin to go high. This is much like a chronograph but I do not need it to measure velocity, just detect the passing of a bullet. Below is a crude (don't laugh) drawing of what it might look like.

I'm using a BPV10NF Photodiode and a TSAL5100 Emitting Diode and cannot get them to be sensitive enough to detect something as small as a bullet to send an Arduino pin high (or low)--even with using a rising or falling edge interrupt (or maybe I'm not writing the sketch correctly).

Requirements:I need help with a basic schematic and parts list along with an Arduino sketch so that I may build it on my home workbench. I am willing to pay someone to help me make this project work; please PM me.

How long will it take for this bullet to pass through this square frame?How long could the bullet obstruct the IR between the emitter and photodiode?In other words, what's the maximum pulse width that could result?[Very short time, very short pulse width - probably too short. Could an Arduino interrupt even notice it?]

"Who is like unto the beast? who is able to make war with him?"When all else fails, check your wiring!

velocity101

How long will it take for this bullet to pass through this square frame?How long could the bullet obstruct the IR between the emitter and photodiode?In other words, what's the maximum pulse width that could result?[Very short time, very short pulse width - probably too short. Could an Arduino interrupt even notice it?]

Not sure what the pulse width would need to be but the bullet would be traveling up to 3,500 feet per second. If not an arduino, any suggestion how to accomplish this with something else?

So, your objective is simply to annunciate1 a projectile's presence in the "window", ideally from as close to its breaking the plane as possible?To me, that would be an Arduino misapplication.

I would look at using:1) an RS Latch (a/k/a SR Latch)http://www.jameco.com/Jameco/Products/ProdDS/13004.pdfpossibly conditioned with a2) a "one-shot" multivibrator [trigger]http://www.jameco.com/Jameco/Products/ProdDS/252259TI.pdf

Still, you need to supply more information.The projectile has some length and travels at some speed, within tolerances, so you should (need to) come up with a figure for how long the detection event will last, even if ideally so.

Can the IRED emitter/detector operate at that speed?

1 - trip an LED, trigger a flash, etc.

"Who is like unto the beast? who is able to make war with him?"When all else fails, check your wiring!

velocity101

So, your objective is simply to annunciate1 a projectile's presence in the "window", ideally from as close to its breaking the plane as possible?To me, that would be an Arduino misapplication.

I would look at using:1) an RS Latch (a/k/a SR Latch)http://www.jameco.com/Jameco/Products/ProdDS/13004.pdfpossibly conditioned with a2) a "one-shot" multivibrator [trigger]http://www.jameco.com/Jameco/Products/ProdDS/252259TI.pdf

Still, you need to supply more information.The projectile has some length and travels at some speed, within tolerances, so you should (need to) come up with a figure for how long the detection event will last, even if ideally so.

Can the IRED emitter/detector operate at that speed?

1 - trip an LED, trigger a flash, etc.

Would you be interested in helping me with this circuit if I paid you?

So a 1 inch long bullet, 25.4mm would be in the frame for some impossibly small number of uS.24.5/(106680000000/uS) = .000000000229uS, something small like that. I'm not sure any logic family will respond to that.A '328 needs a signal to be valid for something 2 clock cycles for it to be captured, 0.13uSBetter option might be shooting thru 2 pieces of foil, let the bullet press the foil together as it passes thru to make a signal that will last longer.

I looked at the specs for a couple of phototransistors and their rise and fall times were 5 usec each, each. So, 5 usec will pass before the photo-t output changes state, but if we assume the worst, 2X (??), 10usec in would still leave us with 8 usec of presence. And that's > than the 0.13usec (min) as stated by CrossRoads.And that doesn't include the processing time to trigger an LED or whatever is supposed to happen as a result.

So, velocity101, what's the "end game"? ** What needs to happen as a result of this detection event? **What's the design goal?

You'll have a row of emitters shining into a row of detectors (AND'ed together or something) and any beam-break (!) results an event?

"Who is like unto the beast? who is able to make war with him?"When all else fails, check your wiring!